42 COLEOPTERA OF NORTH AMERICA. 



Posterior tarsi with, two claws. 2 



Posterior tarsi with a single fixed claw. Ctbister. 



2 Claws equal, or nearly so ; movable ; 3 

 Claws unequal, the upper one fixed (last joint of palpi not elongated) ; 4 



3 Last joint of palpi not elongated. Dytiscus. 

 Last joint of palpi elongated. Eunectes. 



4 Body ovate, intermediate tarsi of male not dilated. Acinus. 

 Body elliptical, intermediate tarsi of male dilated. Hydaticus. 



Fam. v.— gyrinidae. 



Mentum deeply emarginate ; lateral lobes rounded.; gular 

 suture distinct. 



Ligula large, quadrate, corneous, rilling the emargination 

 of the mentum. 



Maxillae with the outer lobe usually wanting, sometimes 

 slender, not articulated, the inner curved, ciliate internally, 

 acute at tip. 



Eyes divided by the sides of the head, upper and lower 

 parts both rounded. 



Antennas inserted under the sides of the front, behind the 

 base of the mandibles, short, thick, third joint auriculate, 

 subsequent ones indistinct, last joint elongate. 



Prothorax with the prosternum short and carinated, epis- 

 terna and epimera distinct, the latter large. 



Mesosternum very large, rhomboidal, posterior angle emar- 

 ginate for the reception of the point of metasternum; episterna 

 and epimera entirely connate, attaining the middle coxae. 



Metasternum very short, pointed before and behind; epis- 

 terna very large; epimera not visible. 



Coxae, anterior, small, globular; middle, flat, oblique, almost 

 reaching to the posterior coxae behind ; the latter are large, 

 truncate anteriorly, contiguous at their inner margin, extend- 

 ing to the margin of the body, and thus separating entirely 

 the ventral segments from the metasternum; they are dilated 

 internally, and broadly excavated behind for the motion of 

 the hind legs. 



Abdomen 7-jointed, the three anterior segments connate, 

 the first almost obsolete ; the seventh longer than the sixth, 

 rounded at tip. 



Anterior legs very long, received in oblique grooves of 

 the pro- and mesosternal segments; tibiae slender, with one 

 terminal spur; tarsi 5-jointed, of the male sometimes dilated. 



